At what point in P90x should results really start to kick in?

There is a structure that is designed for you to see the greatest results in the latter part of the program. Essentially, each block is designed to have an adaptation phase, followed by a growth (or mastery) phase. In between we have recovery (that are more like transition phases). Because even the transition phases are hard, you body is in a constant state of adaptation throughout the beginning of the program (varies with indivudual but this is the general plan), that is designed for you to peak late in the program.

In any program you plan for a peak. X is designed to peak late. Once you've adapted to a set routine you have a short peak period where fitness gains happen very rapidly. In a perfect world, we've set this up to happen in block three. And this is where most people make the greatest improvements.

As an example, during our initial test group there was nearly a mutiny due to lack of gains. This was because our small group (4 people) was in breakdown through the first two stages and weren't seeing great results. The all wanted us (me and Tony) to alter the schedule of the program. I drew a chart on a blackboard, showing them what was supposed to happen. Tony backed me up and the program stayed as designed. All of those people's results went nuts during block three and they stopped complaining.